The conventional auto tensioners are of a structure having a function of regulating the movement of a tension pulley so that a vibration and impact from a belt are attenuated while allowing the movement of the tension pulley according to the tensile force of the belt generated by temperature variations in the environment, changes caused by an expansion or contraction over time, or the like.
One of such auto tensioners is disclosed in the Unexamined Published Japanese Patent Application No. H11-133955, which relates to the application by the Applicant. The auto tensioner has an arm for supporting a tension pulley. An annular friction plate is sandwiched between the end face on the front side of the boss portion of the arm and a guide plate integrally fitted to the front end of a support shaft for supporting the arm so that the extension restoring force of a helical torsion coil spring has the friction plate pressure-contact with the boss portion and the guide plate.
In the case of the foregoing type of an auto tensioner, the respective sliding portions between the friction plate, boss portion and guide plate occasionally suffer a succession of behaviors such as sticking to one another or slipping, generally termed as the stick-slip, depending on how the load from the extension restoring force of the helical torsion coil spring is imposed and the status of the movement and vibration of the tension pulley. The generation of the stick-slip phenomenon causes the guide plate made of steel plate to vibrate, which results in generation of an unusual sound or noise in the auto tensioner.
As a technique to control generation of such an unusual sound or noise in the auto tensioner, the thickness of the guide plate made of steel plate can conceivably be increased. However, materials of high rigidity such as a steel plate or the like have disadvantages of poor attenuation of a vibration and a natural resonance caused by the vibration, thereby generating a secondary noise or the like. Therefore, in terms of controlling the vibration of the guide plate due to the stick-slip and the consequent reduction of the unusual sound and noise in the auto tensioner, there can be no good results expected from merely increasing the thickness of the guide plate. Further, to increase the thickness is not preferable leading to an increased weight of the auto tensioner.
Therefore, a main object of the present invention is to provide an auto tensioner capable of reducing an unusual sound or noise generated by the vibration of the guide plate subject to the stick-slip in the sliding portions of an arm for supporting a tension pulley.